cygwin issues

[Bryce McKinlay]

Tony Kimball wrote:

> - Link arguments are wrong, out of the box:
>   libgcjdata.a and -lpthread are supplied to collect2.  I just work
>   around this so far.

We should move the defination of THREADSPEC and THREADLIBS from
configure.in to configure.host so it can be changed for different
targets.

> - alloca.  ok, this should be obvious to me, but its not.  There's
>   seemingly no alloca.h for cygwin, so I just changed references to
>   __builtin_alloca.

I think thats a reasonable fix. We only build on one compiler so we know
__builtin_alloca is availble.

regards

  [ bryce ]